The impacts of transport emissions on air quality in Auckland’s city centre

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The City Centre area is the rapidly expanding economic, social and cultural heartland of Auckland. Unfortunately, it is also where Auckland’s highest air pollution levels are observed. Narrow roads flanked by high buildings create deep street canyons that restrict ventilation of air pollutants such as nitrogen dioxide (NO2) and fine particulate matter 2.5 micrometres and smaller (PM2.5) resulting in levels which sometimes exceed national and international regulatory standards for air quality. This is despite an otherwise favourable geographical location that encourages a reliable airflow and has little long-range transportation of pollutants from neighbours.

An awareness of the impacts of air pollution along with a recognition of Auckland’s climate change commitments has helped focus attention on the impacts of policy implementation on air quality. Key stakeholders require evidence to help guide strategy development that is consistent with the local climate, urban design and environmental goals. Policy decisions that promote safer streets, climate action, active and public transportation modes as well as congestion mitigation strategies have multiple and interdependent benefits. These include increased economic activity, vibrant social spaces and a cleaner, more sustainable environment, including cleaner air.

All fossil fuelled vehicles degrade air quality to some extent. However, diesel vehicles tend to emit higher concentrations of air pollutants than petrol vehicles. Multiple studies have drawn attention to the relationship between the volume of bus traffic and elevated concentrations of NO2 and black carbon. Black carbon is a component of fine and ultra-fine particulate matter produced during diesel fuel combustion. These very small airborne particulates have been connected to chronic and acute health impacts world-wide and are a concern in an area of Auckland that has over 10 million pedestrians a year. Studies indicate that a key method of reducing air pollution in Auckland’s City Centre is to reduce emissions from buses and other large heavy goods and construction vehicles. Evidence provided in this report demonstrates multiple benefits to proposed traffic calming, bus electrification and street pedestrianisation projects across downtown Auckland.